The present invention relates to a deployable diverging part for a thruster.
It is well known in a thruster, in particular in a second or third stage of a multistage launcher, to use a rocket engine nozzle that has a deployable diverging part. The idea is that by deploying the diverging part in flight, the outlet section of the nozzle can be adapted as a function of ambient pressure, which ambient pressure diminishes from low altitudes close to the ground to high altitudes on leaving the earth""s atmosphere. As a result, optimum thrust can be obtained at altitude while limiting size on the ground.
Usually, a deployable diverging part comprises a first portion which constitutes the entire diverging part in its initial configuration and which can be lengthened by installing one or more diverging rings. The or each diverging ring is moved from a retracted position in which it surrounds the first portion of the diverging part to a deployed position in which it connects to the downstream end of the first portion or of a previously-installed diverging ring.
Various mechanisms have been proposed, all of which seek to ensure that deployment takes place automatically and reliably with a minimum expenditure of energy. Deployment mechanisms based on articulated arms are described in particular in document EP-A-0 516 519 and in French patent application FR-2743110 in the name of the Assignee. Other mechanisms, e.g. based on telescopic arms, on screws, on roll-out beams, or on membranes are also known.
The deployment mechanism can be activated by actuator means that do not require an external energy source, e.g. spring devices, or by means such as actuators or motors which require a source of electrical or hydraulic energy or indeed a gas generator.
Spring devices are used when deployment takes place prior to ignition, however they turn out generally to be inadequate for achieving reliable deployment after ignition because of the action of the ejected gases. It is then necessary to use motors or actuators that develop higher power.
It is desirable for the energy requirements to be kept as small as possible, and the present invention seeks specifically to provide a deployable diverging part that requires only a small amount of power for deployment, and that can therefore be deployed after ignition without recourse to an external energy source, e.g. merely by means of springs.
This object is achieved by a deployable diverging part for a thruster, the part comprising a first portion, at least one second portion in the form of diverging ring displaceable between a retracted position in which it surrounds the first portion and a deployed position in which it is connected to a downstream end of the first portion, a deployment mechanism capable of causing the first diverging ring to pass from its retracted position to its deployed position, and actuation means for actuating the deployment mechanism, the diverging part being characterized in that a temporary structure, or xe2x80x9cinsertxe2x80x9d, is disposed inside the diverging ring so as to transform the diverging section thereof into a non-diverging section, at least over the major fraction of the length of the diverging ring, the insert being eliminatable on or after the diverging ring coming into its deployed position.
By offering a surface that is non-diverging, and which is preferably substantially cylindrical, to the combustion gas flowing in the diverging part, the insert makes it possible to reduce considerably the amplitude of the axial force component acting on the diverging ring and opposing deployment thereof, i.e. the component that is directed upstream (in the present text, the terms xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d are used relative to the flow direction of the combustion gas in the diverging part).
Since the deployment force is considerably reduced, it is possible to use energy storage means for actuation purposes, e.g. spring devices, without any connection to an external energy source, even for deploying the diverging part after ignition.
When the diverging part has a plurality of deployable diverging rings associated with respective deployment mechanisms and actuation means, each diverging ring is advantageously provided with its own insert.
The insert can be connected to the diverging ring by mechanical link means which are released or broken on or after the diverging ring coming into its deployed position so as to enable the insert to be expelled. The link means are advantageously released by means of at least one release member that is displaceable between a first position in which the link means are locked and a second position in which the link means are released, the release member optionally being moved automatically by contact with the diverging part when the diverging ring comes into its deployed position. The link means can be broken by pyrotechnic means, after the diverging ring has come into its deployed position.
In a variant, the insert is connected to the diverging ring by link means that are made at least in part out of a material of strength that is ephemeral in the combustion gas flowing through the diverging part, thus enabling it to be eliminated after the diverging ring has come into its deployed position, so as to enable the insert to be expelled.
Advantageously, at least one spring element is interposed between the inside wall of the diverging ring and the insert and it applies a force on the insert that has at least an axial component directly downstream so as to facilitate expulsion of the insert after the link means have been released, broken, or eliminated.
In yet another variant, the insert itself is made at least in part out of a material whose strength is ephemeral in the combustion gas flowing through the diverging part, so that it is eliminated after the diverging ring has come into its deployed position.